gas burner apparatus with pre-mixing

ABSTRACT

A gas burner apparatus with pre-mixing includes a mixing device for mixing an air/gas mixture which is intended to be conveyed to the intake section of a fan unit whose delivery is conveyed to a combustion head of the burner. The mixing device including a plurality of ducts, each of which has a region in the form of a Venturi duct with contiguous portions which are convergent/divergent, with respect to the direction of flow, and with a restricted duct cross-section defined between the convergent portion and the divergent portion, there being conveyed in each convergent portion an air flow which is intended to be mixed with a gas flow which is introduced into the duct at the restricted cross-section, the air/gas mixture being conveyed through the divergent portion of the duct to the intake section of the fan unit. Each duct of the plurality is defined by the engagement of at least a first and a second mutually separate burner region along a mutual engagement profile, there being carried on each of the burner regions corresponding, separate portions of each of the ducts, at least a first fluid-tight sealing element being provided between the burner regions along the engagement profile in order to prevent gas and/or air from being drawn in with respect to the ducts. The at least first sealing element is interposed between the burner regions at the restricted cross-section of each of the Venturi ducts of the plurality of ducts; the at least first sealing element has through-holes which define the restricted cross-section of the corresponding Venturi duct in at least some of the plurality of ducts, as a result of the engagement of the burner regions along the engagement profile and is interchangeable with at least a second sealing element which has corresponding through-holes, whose overall size for the relevant cross-sections is different from the overall size for the cross-sections relating to the corresponding holes of the first sealing element, so as to vary the overall cross-section defined by the plurality of holes of the ducts, with at least the first element being interchanged with at least the second sealing element, and consequently to control the burner in accordance with the thermal power required and/or the flow resistances which exist in the ducts for supplying the air/gas mixture to the burner.

TECHNICAL FIELD

The present invention relates to a gas burner apparatus with pre-mixinghaving the features set out in the preamble of claim 1.

TECHNOLOGICAL BACKGROUND

In the specific technical sector, it is known to construct gas burnersof the pre-mixing type, for example, for condensation boilers, whosecombustion head is intended to be received in a combustion chamber, towhich the air/gas mixture is supplied by means of the delivery of a fanunit. An example of such a burner apparatus is known from Italian PatentApplication No. PD2007A000413, in which there is described a burnerwhich is connected to a cover or another similar closure element of thecombustion chamber and in which there are coaxially mounted a fan unitand a cap-like combustion head. In such an application, the air/gasmixture which is burnt is at the surface of the combustion head of theburner is in the form of a plurality of mixing ducts which are opentowards the outer side of the burner in order to draw in air and throughwhich the air, once mixed with the gas, is directed towards the intakesection of the fan. Each of those ducts generally functions underreduced pressure, with the fan positioned downstream and is in the formof a Venturi duct, that is to say, which is formed by a convergentportion which is contiguous relative to a divergent portion, betweenwhich there is defined a minimum cross-section of the Venturi duct, areduction in the pressure signal (pressure reduction) being produced inthat cross-section. That signal is typically used to draw in from thevalve the combustible gas which is then introduced into the mixing ductin order to then become mixed with the air drawn in by the reducedpressure.

The pressure signal which is generated in the minimum cross-section ofthe Venturi duct is further a function of various parameters. Forexample, if the number of revolutions of the fan increases, for a givengeometry, a greater flow of air is drawn in with a greater velocitythrough the minimum cross-section and therefore a greater pressurereduction is consequently generated. Furthermore, if the flowresistances downstream of the fan change, the signal changes as aresult. For example, if the flow resistances increase, the signaldecreases and, in order to be able to maintain it at the levels beforethe increase in the flow resistances, it is normally necessary to useanother Venturi duct having a smaller minimum cross-section. However,this results in a cost increase because it requires the production andcontrol of additional components in the burner. That problem isparticularly apparent in applications in which the range of adjustmentof the thermal output means that such components have to be replaced forcorrect adjustment of the burner.

STATEMENT OF INVENTION

The problem addressed by the present invention is to provide a burnerapparatus which is structurally and functionally configured so as toallow the limitations set out with regard to the cited prior art to beovercome. This problem is solved by the invention by means of a burnerapparatus constructed in accordance with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be betterappreciated from the following detailed description of one preferredembodiment thereof which is illustrated by way of non-limiting examplewith reference to the appended drawings, in which:

FIG. 1 is a partially sectioned, perspective view of a burner apparatusconstructed in accordance with the present invention,

FIG. 2 is a schematic view of a detail of the burner of FIG. 1,

FIG. 2A is a schematic view of another detail of FIG. 1,

FIGS. 3 and 4 are partially sectioned, perspective views of a detail ofthe preceding Figures in separate assembly steps,

FIGS. 5 and 6 are front elevation views of a detail of FIG. 4 in twoseparate construction forms,

FIG. 7 is another front elevation view of another construction variantof the detail of FIGS. 5 and 6.

PREFERRED EMBODIMENT OF THE INVENTION

With reference to the Figures set out, a gas burner apparatus withpre-mixing constructed in accordance with the present invention isgenerally designated 1.

The burner comprises a combustion head 2, preferably having a cap-likeconstruction whose base is advantageously secured to a cover 3 whichconstitutes a closure element of a combustion chamber (not illustrated)which is associated with the burner.

A fan unit 4, whose impeller 5 of the centrifugal type is coaxial withthe combustion head, is further rotatably supported on the cover. Theaxis of rotation of the impeller, which is actuated by an electric motor6, is designated X.

Behind the combustion head 2 and internally with respect thereto, thereis provided a distribution element which is designated 7 and which isalso substantially of cap-like form and is provided with through-holesfor distributing the air/gas mixture to the combustion head.

There remains defined in the body of the burner, between thedistribution element 7 and the impeller 5 facing it, an internal spaceor volume which is generally designated 8 and in which there areconveyed, in a separate and distinct manner, the mixture which is fromthe delivery cross-section 9 of the fan and which is directed to thedistributor 7, and the flow of the air/gas mixture which is directed tothe intake section 10 of the fan. Such a burner structure is describedin detail in the Italian patent application which is referred to aboveand filed under number PD2007A000413, to which reference is made hereconcerning any details which are not expressly set out below.

More specifically, there are provided a first plurality of conveyingducts which are designated 11 and which are capable of conveying thecombustible air/gas mixture to the combustion head 2 which is suppliedby way of the delivery side 9 of the fan and a second plurality ofconveying ducts 12 which are suitable for conveying the flow of airand/or gas which is taken from outside the burner body in the directionof the intake section 10 of the fan. That intake section is arranged atthe same side of the head 2 and is in communication with a first chamber13 which is defined in the volume space 8 which remains between the head2 and the impeller 5. The pluralities of ducts 11 and 12 are furtherselected in terms of size and structure so that the flow of the air/gasmixture to the delivery side of the fan intersects with the flow of airand/or gas which is directed to the intake section, as schematicallyillustrated in FIG. 2, in which the above-mentioned flows are conveyedso as to be separate and distinct from each other by the ducts 11 and12, respectively.

The ducts 11 of the corresponding plurality extend in the region of thedelivery section 9 of the fan, outside the outer diameter of theimpeller 5, in order to connect that delivery section to a secondchamber 14 for distributing the mixture, which chamber 14 is alsodefined in the space 8 between the distributor 7 and the impeller and isseparated from the chamber 13 by means of a wall 15.

The ducts 11 are distributed circumferentially, downstream of thedelivery section 9, with a pre-selected angular interval, in particularwith a regular angular interval. Each of the ducts 11 further has, withrespect to the direction of flow, an inlet opening 11 a for the mixture(provided from the delivery side of the fan), in which the flow has aprevailing radial component, and a discharge opening 11 b, at theopposite end, in which the flow has a prevailing axial component.Downstream of the discharge opening, the chamber 14 is configured so asto further deviate the flow in order to convey it along the distributor7 in order to efficiently supply the combustion head 2.

The second plurality of conveying ducts 12 is configured in order togenerate pre-mixing of the air, taken from outside, with the gas whichis introduced into the duct and thereby to convey a pre-mixed air/gasflow to the intake section 10 of the fan.

The ducts 12 are arranged in an alternating position with respect to theducts 11 in such a manner that, in the region of intersection of theflows, designated M in FIG. 2, each duct 12 is interposed between a pairof ducts 11 which are adjacent to each other.

Each duct 12 is open at the outer side of the burner, at the intakesection 12 a of the duct, by way of which a flow of air is drawn in andextends as far as an opposite discharge section 12 b which is placed incommunication with the intake section 10 of the fan. Only one of theducts 12 will be described in detail below, because they are ofidentical construction.

Each duct 12 is provided with mixing means, which comprise a portion ofthe duct itself that is configured as a Venturi duct, that is to say,comprising a convergent portion 16 a which extends into a contiguous,divergent portion 16 b, there remaining defined between the portions arestricted section (minimum section) of the Venturi duct, designated 16c. At that minimum section 16 c, there is introduced a flow of gas intothe Venturi duct, drawn in by the reduced pressure brought about in theminimum section. The duct is designated 17 and continues in the form ofa valve 18, which is only schematically illustrated and which is capableof conveying the combustible gas into the corresponding duct 12, at thatminimum section 16 c. FIG. 2A is a purely schematic view of thepre-selected configuration in relation to the Venturi duct.

Each duct 12 is further formed following the engagement of a firstregion and a second region of the burner, which are separate from eachother, along a surface engagement profile, the first region which isgenerally designated A being defined in the base structure of the cover3 which extends axially upstream of the impeller, the second regionwhich is generally designated B being arranged downstream of theimpeller and in which the wall 15 is arranged in the delivery zone ofthe burner. There is interposed between the burner regions A and B afluid-tight sealing element which is designated 20 and which has themain function of preventing gas and/or air from being drawn in betweenthe ducts 11 and 12 in a relative manner.

The sealing element 20 is advantageously of planar annular form withreduced transverse thickness, as clearly shown in FIG. 4. According to amain feature of the invention, that sealing element is positioned at therestricted sections 16 c of the ducts 12 (minimum section of the Venturiduct). The sealing element 20 is further provided, in the annular wallthereof, with a plurality of through-holes which are all designated 21and which define the restricted section of the corresponding Venturiduct at least in some of the plurality of ducts 12, once the regions Aand B of the burner have been engaged along the engagement profilethereof, with the seal 20 being interposed.

With reference to FIG. 5, the through-holes 21 are arrangedcircumferentially with a regular angular interval along the annular wallof the seal 20. They have, when viewed in cross-section, a substantiallydrop-like shape. A corresponding through-hole 22 having the shape of thecross-section extending in a prevailing direction, as clearly shown inFIG. 5, is provided and is associated in an adjacent position withrespect to each hole 21. Those holes 22 define the sections of passageof the gas flow, for each of the ducts 17, at the restricted section ofthe Venturi duct, where there occurs the introduction of the combustiblegas into the air flow which is conveyed by the ducts 12.

In greater detail, each duct 17 is, upstream of the seal 20, incommunication with a channel 17 a which extends in an annular manner inthe burner region A, concentrically relative to the axis X, which servesto distribute and convey the gas from the valve in each of the ducts 17.The channel 17 a is jointly defined by the burner region A and the seal20 which is contiguous therewith.

There is further defined in the sealing element 20 another plurality ofthrough-holes which are all designated 23 and which delimit thecross-section of passage of the flow of the air/gas mixture which issupplied by the delivery 9 of the fan and which is directed to thedistributor 7 of the combustion head. In other words, those holes 23define the cross-section of each of the ducts 11, in the region of theseal 20, and are positioned along the circumferential profile of theseal, in alignment with the holes 21 with a pre-selected, regular,angular interval. In the preferred embodiment of FIG. 5, there isprovision for the holes 23 to be provided in an alternating manner withrespect to the holes 21, along a common circular profile which isconcentric relative to the axis X so that each hole 23 is interposedbetween a pair of mutually adjacent holes 21, as clearly illustrated inFIG. 5.

In accordance with a main feature of the invention, the sealing element20 is configured so as to be interchangeable with at least a secondsealing element which is designated 20′ (illustrated in FIGS. 4 and 6)and which is provided with a plurality of through-holes 21′ having thesame function as the corresponding holes 21 of the seal 20, the overallsize of the cross-sections of those holes 21′ being different (greateror smaller than) from the overall size of the cross-sections relating tothe holes 21′. In that manner, by the seal 20 being interchanged withthe seal 20′, it is possible to vary the overall section relating to theflow of air which is drawn into the burner in order to consequentlyadjust the burner in accordance with the thermal output required and/orthe flow resistances which exist in the supply ducts of the air/gasmixture.

It will be appreciated that the invention allows the provision of aplurality of sealing elements with the number and shape of the holes 21which are advantageously pre-selected in accordance with therequirements for adjustment and the power intervals required for theoperation of the burner. Reference will be made below only to a secondinterchangeable sealing element, it being possible to provide aplurality of mutually interchangeable seals.

In a first preferred embodiment, there is provision for there to be thesame number of holes 21, 21′ and 23, 23′ in the seal 20 and 20′ andalternating positioning in each of those seals, as described above andillustrated in FIGS. 5 and 6, respectively. The holes 21 are furtherequally spaced apart from each other, as are the holes 21′, 23 and 23′.

The second sealing element 20′ differs from the seal 20 in that thereare provided holes 21′ each having a cross-section of greater size thanthe size of each corresponding hole 21 of the seal 20.

In a variant of the seal 20′, generally designated 20″, there caninstead be provision for the number of holes 21″ to be different fromthe number of holes 21′, but with the holes 21′ and 21″ having the samecross-section. In FIG. 7, which illustrates that variant, it is clearlyshown how there are provided only six holes 21″, unlike the seal 20′which has nine corresponding holes 21′. As a result, for a givencross-section of the holes 21′ and 21″, the overall section varies whenthe seal 20′ is interchanged with the seal 20″.

Naturally, other construction variants are possible, all directedtowards the provision of different configurations of calibrated holesfor the passage of intake air, in the restricted section of the Venturiduct, for each of the seals which are provided and which are mutuallyinterchangeable, in such a manner as to generate the desired pressuresignal and in order to control the gas valve. Advantageously, it ispossible in that manner to ensure wide modulation in accordance with thethermal power required, for each power range, simply by the sealingelement being interchanged, without any other additional components andwithout any modification of the other structural components of theburner both at the side of the cover and at the delivery side. As aresult, therefore, control of the burner apparatus is simplified andfacilitated, even in the presence of broad modulation ranges that arerequired for the thermal power of the apparatus.

It is further possible, if considered advantageous, to provide forthrottling of the passage sections of the gas in the ducts 17, by way ofdifferent provision (concerning the number and size of the section) ofthe holes 22 in each of the sealing elements which may be provided andwhich can be mutually interchanged.

The invention thereby solves the problem set out, resulting in theadvantages set out above in relation to known solutions.

1. A gas burner apparatus with pre-mixing comprising mixing device formixing an air/gas mixture which is intended to be conveyed to the intakesection of a fan unit, whose delivery is conveyed to a combustion headof the burner, the mixing device comprising a plurality of ducts, eachof which has a region in the form of a Venturi duct with contiguousportions which are convergent/divergent, with respect to the directionof flow, and with a restricted duct cross-section defined between theconvergent portion and the divergent portion, there being conveyed ineach convergent portion an air flow which is intended to be mixed with agas flow which is introduced into the duct at the restrictedcross-section, the air/gas mixture being conveyed through the divergentportion of the duct to the intake section of the fan unit, each duct ofthe plurality being defined by the engagement of at least a first and asecond mutually separate burner region, along a mutual engagementprofile, there being carried on each of the burner regionscorresponding, separate portions of each of the ducts, at least a firstfluid-tight sealing element being provided between the burner regionsalong the engagement profile in order to prevent gas and/or air frombeing drawn in with respect to the ducts, the at least first sealingelement is interposed between the burner regions at the restrictedcross-section of each of the Venturi ducts of the plurality of ducts, inthat the at least first sealing element has through-holes which definethe restricted cross-section of the corresponding Venturi duct in atleast some of the plurality of ducts, as a result of the engagement ofthe burner regions along the engagement profile, and in that at leastthe first sealing element is interchangeable with at least a secondsealing element which has corresponding through-holes, whose overallsize for the relevant cross-sections is different from the overall sizefor the cross-sections relating to the corresponding holes of the firstsealing element (20), so as to vary the overall cross-section defined bythe plurality of holes of the ducts, with at least the first elementbeing interchanged with at least the second sealing element, andconsequently to control the burner in accordance with the thermal powerrequired and/or the flow resistances which exist in the ducts forsupplying the air/gas mixture to the burner.
 2. A burner apparatusaccording to claim 1, wherein at least the first sealing element andsecond sealing elements which are mutually interchangeable are ofannular shape and the through-holes which are provided in eachcorresponding sealing element are provided so as to be circumferentiallyand angularly spaced apart from each other.
 3. A burner apparatusaccording to claim 1, wherein the holes which are provided in the firstsealing element all have the same predetermined size for thecross-section and the holes which are provided in the second sealingelement all have the same predetermined size for the cross-section,which is different from that provided in the first sealing element.
 4. Aburner apparatus according to claim 3, wherein the holes in the firstsealing element are provided so as to be equal in number to the holes ofthe second sealing element.
 5. A burner apparatus according to claim 1,wherein each hole of the first element has a size for the cross-sectionthat is equal to that of the cross-section of each hole of the secondsealing element, and the total number of holes of the first element isdifferent from the total number of holes of the second sealing element.6. A burner apparatus according to claim 1, wherein the holes which areprovided in the first sealing element and second sealing element areregularly spaced apart from each other with a predetermined angularinterval.
 7. A burner apparatus according to claim 1, wherein there isprovided, by means of the holes of the corresponding sealing element,the passage for the flow of air which is drawn into the burner, withcorresponding second, separate holes being provided in the sealingelements and defining the cross-section of passage of the gas flow whichis introduced into the restricted cross-section of each Venturi duct. 8.A burner apparatus according to claim 7, wherein there is provided, foreach sealing element, a hole for the passage of gas in a positionadjacent to a corresponding hole for the passage of intake air.
 9. Aburner apparatus according to claim 1, wherein there are provided, ineach of the sealing elements, a plurality of third through-holes whichdefine the cross-section of passage, at the engagement profile of theburner regions, of ducts which are capable of conveying flows of theair/gas mixture which are supplied from the delivery side of the fanunit in the direction of the burner head.
 10. A burner apparatusaccording to claim 9, wherein the third holes are circumferentiallyarranged in each of the sealing elements, alternating with the holes forthe passage of the intake air.